When Luigi comes in contact with Blue Mice or Purple Mice, he drops two coins and loses five health points. Purple Mice have the ability to crawl on walls, while Blue Mice are incapable of doing so.

There is a related enemy called the Gold Mouse. This mouse releases treasure when sucked inside of Luigi's Poltergust 3000. It hides in some rooms and has a twenty percent chance of appearing upon entrance; it alternatively can be found in a block of cheese that can only be seen and scanned by Luigi's Game Boy Horror.